A solar cell with a property of semiconductor converts a light energy into an electric energy.
A structure and principle of the solar cell according to the related art will be briefly explained as follows. The solar cell is formed in a PN-junction structure where a positive(P)-type semiconductor makes a junction with a negative(N)-type semiconductor. When a solar ray is incident on the solar cell with the PN-junction structure, holes(+) and electrons(−) are generated in the semiconductor owing to the energy of the solar ray. By an electric field generated in an PN-junction area, the holes(+) are drifted toward the P-type semiconductor, and the electrons(−) are drifted toward the N-type semiconductor, whereby an electric power is produced with an occurrence of electric potential.
The solar cell can be largely classified into a wafer type solar cell and a thin film type solar cell.
The wafer type solar cell uses a wafer made of a semiconductor material such as silicon. In the meantime, the thin film type solar cell is manufactured by forming a semiconductor in type of a thin film on a glass substrate.
With respect to efficiency, the wafer type solar cell is better than the thin film type solar cell. However, in the case of the wafer type solar cell, it is difficult to realize a small thickness due to difficulty in performance of the manufacturing process. In addition, the wafer type solar cell uses a high-priced semiconductor substrate, whereby its manufacturing cost is increased.
Even though the thin film type solar cell is inferior in efficiency to the wafer type solar cell, the thin film type solar cell has advantages such as realization of thin profile and use of low-priced material. Accordingly, the thin film type solar cell is suitable for a mass production.
The thin film type solar cell is manufactured by sequential steps of forming a front electrode on a glass substrate, forming a semiconductor layer on the front electrode, and forming a rear electrode on the semiconductor layer. In this case, since the front electrode corresponds to a light-incidence face, the front electrode is made of a transparent conductive material, for example, ZnO. With the increase in size of substrate, a power loss increases due to a resistance of the transparent conductive layer.
Thus, a method for minimizing the power loss has been proposed, in which the thin film type solar cell is divided into a plurality of unit cells connected in series. This method enables the minimization of power loss caused by the resistance of the transparent conductive material.
Hereinafter, a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series will be described with reference to FIGS. 1A to 1G.
FIGS. 1A to 1G are cross section views illustrating a related art method for manufacturing a thin film type solar cell with a plurality of unit cells connected in series.
First, as shown in FIG. 1A, a front electrode layer 20a is formed on a substrate 10, wherein the front electrode layer 20a is made of a transparent conductive material, for example, ZnO.
As shown in FIG. 1B, a plurality of front electrodes 20 are formed by patterning the front electrode layer 20a, wherein the plurality of front electrodes 20 are provided at fixed intervals by each first separating portion 21 interposed in-between.
As shown in FIG. 1C, a semiconductor layer 30a is formed on an entire surface of the substrate 10 including the front electrodes 20.
As shown in FIG. 1D, a plurality of semiconductor layers 30 are formed by patterning the semiconductor layer 30a, wherein the plurality of semiconductor layers 30 are provided at fixed intervals by each contact part 35 interposed in-between.
As shown in FIG. 1E, a rear electrode layer 50a is formed on an entire surface of the substrate 10.
As shown in FIG. 1F, a plurality of rear electrodes 50 are formed by patterning the rear electrode layer 50a, wherein the plurality of rear electrodes 50 are provided at fixed intervals by each second separating portion 51 interposed in-between. When patterning the rear electrode layer 50a, the semiconductor layer 30 positioned underneath the rear electrode layer 50a is patterned together.
As shown in FIG. 1G, an isolating part 55 is formed by patterning the outermost front electrode 20, the outermost semiconductor layer 30, and the outermost rear electrode 50, thereby completing the process for manufacturing the thin film type solar cell.
During a modular process of the completed thin film type solar cell, a predetermined housing is connected with the thin film type solar cell. At this time, the outermost isolating part 55 prevents a short from occurring between the housing and the thin film type solar cell.
For forming the isolating part 55, a laser-scribing process is necessarily performed. In this case, if the front electrode 20 and rear electrode 50 are removed completely as shown in the left-side outermost portion of FIG. 1G, it makes no problems. However, if the front electrode 20 and rear electrode 50 are removed incompletely as shown in the right-side outermost portion of FIG. 1G, the remaining front electrode 20 and rear electrode 50 may be partially melted and connected with each other by laser beams. According as the melted front electrode 20 and rear electrode 50 are connected with each other, the short may occur therein, whereby the corresponding unit cell can not perform a cell function.